Lithography is a key process in the fabrication of semiconductor integrated circuits. Photolithography typically involves projecting an image through a reticle or mask onto a thin film of photoresist or other material that covers a semiconductor wafer or other substrate, and developing the film to remove exposed or unexposed portions of the resist to produce a pattern in subsequent processing steps. In semiconductor processing, the continual shrinking in feature sizes and the increasing development of nanoscale mechanical, electrical, chemical and biological devices requires systems to produce nanoscale features. However, with conventional photolithography using light, the minimum feature size and spacing between patterns is generally on the order of the wavelength of the radiation used to expose the film. This limits the ability to produce sub-lithographic features of about 60 nm using conventional lithography.
Microcontact printing has been developed to create sublithographic features in semiconductor devices. This technique generally involves stamping or pressing a soft template or stamp bearing small scale topographic features onto a receptor substrate to form a pattern on the substrate. The features on the template are typically prepared by photolithography or electron (e-beam) lithography. For example, FIG. 1 illustrates a conventional soft template or stamp 10 formed, for example, from polydimethylsiloxane, with defined features 12 structured with a stamping surface 14 and sidewalls 16. The stamping surface 14 defines a dimension (d) of the pattern to be stamped onto a substrate. As shown in FIG. 2, the features 12 of the stamp are wetted with an ink 18 that is physisorbed or chemisorbed onto the stamping surface 14 and the sidewalls 16 of the features 12. As depicted in FIG. 3, the inked stamp 10 is brought into contact with a receptor substrate 20 (e.g., silicon wafer) and the ink 18 is transferred to regions of the substrate 20 where the ink 18 forms self-assembled monolayers (SAMs) 22 (FIG. 4).
However, resolution of small features is problematic because of inconsistent printing due to capillary forces that pull ink 18 sorbed to surfaces of the features 12 adjacent to the stamping surface 14 (e.g., the sidewalls 16) onto the substrate 20 (e.g., areas 24). Such wicking of the ink 18 material onto the substrate 20 also alters the intended dimension (d) of the stamped features (SAMs) 22, as defined by the stamping surfaces 14 of the stamp/template. In addition, the size and dimension of the stamped features 22 on the receptor substrate 20 are limited to the dimensions (d) of the lithographically formed features 12 defined on the stamp.
Other processes such as e-beam lithography and extreme ultraviolet (EUV) lithography have been used in attempts to form sub-lithographic features. However, the high costs associated with such lithographic tools have hindered their use.
Self-assembled block copolymer films have been prepared by patterning the surface of a substrate with chemical stripes (chemical templating), each stripe being preferentially wetted by the alternate blocks of a block copolymer. A block copolymer film with lamellar morphology, a periodicity matching the stripe pattern and both blocks being neutral wetting at the air interface (e.g., PS-PMMA) that is cast on the patterned substrate and thermally annealed will self-assemble so that the domains orient themselves above the preferred stripes and perpendicular to the surface. However, the process has no advantage over EUV lithography or other sub-lithographic patterning techniques since one of these patterning techniques must be used to form the substrate template pattern, and with the use of expensive patterning tools, the low-cost benefits of using block copolymers are lost.
It would be useful to provide a method and system for preparing sub-lithographic features that overcome existing problems.